1. Field of the Invention
The present invention relates to tractors. In particular, the present invention relates to battery-powered electric tractors.
2. Description of the Prior Art
Across the United States and throughout the world, agricultural tractors are used to plow fields, plant seed, harvest crops and perform countless other chores. Indeed, these vehicles are extremely versatile and well suited for use within the often harsh agricultural environment. Modern tractors are almost exclusively powdered by internal combustion engines which run on petroleum-based fuels. The diesel engine has in fact become the most popular power source for agricultural tractors. These engines provide acceptable power output characteristics and, until recently, fuel has been readily available, even though relatively expensive.
The characteristics of tractors powered by internal combustion engines are, however, less than ideal. Operating expenses are heavily dependent upon the price of fuels. Gasoline and diesel fuel prices have been rising sharply in recent years, greatly increasing the operating expenses. Extensive use within harsh environments often results in mechanical failures. Internal combustion engines on tractors also require a great deal of complicated and expensive maintenance. Diesel engines are also very difficult to start during cold weather. Tractor "down time" due to these factors can be very expensive for a farmer, especially when they occur during critical time periods.
It is undesirable to use tractors driven by internal combustion engines for many farmyard tasks. Extensive work within enclosed buildings is often required. Hazards posed by exhaust fumes severely restrict the use of tractors powered by internal combustion engines for these applications. Livestock are easily disturbed by the noise of internal combustion engines. It is, therefore, undesirable to use tractors of this type for chores performed in close proximity to livestock.
Although diesel engines do provide some degree of torque "back up" with reduced engine speed, their power output characteristics are less than ideal. Another problem is that the power-take-off (PTO) which is used to drive implements attached to a tractor is typically driven by the main tractor engine. Even though the PTO may be driven through a separate transmission, its operating speed is a function of tractor engine speed. This can result in undesired limitations on the speed at which an operator can run the implements.
Potential uses for an electric battery-powered tractor are becoming more evident every day. A study by Resen et al entitled "Electric Vehicles--Assessment of Potential as it Relates to Farm Size," A.S.A.E. Paper NCR80-201 (1980), has suggested that up to half of all tasks on eastern South Dakota farms could be performed by a battery-powered tractor. Similar projections were made for farms throughout the United States. Current research indicates that battery-powered tractors are especially well suited for "chore-type" tasks, such as hauling, scraping, feedlot operation and the like.
In a paper entitled "State-of-the-Art Assessment of In-Use Electric and Hybrid Vehicles," DOE/TIC-10231 (1979), the Department of Energy concluded that electric vehicles have a useful operating life far longer than vehicles with internal combustion engines. In general, electric vehicles require much less maintenance than those powered by internal combustion engines. Reduced maintenance expenses and "down time" are significant.
Electric vehicles are extremely easy to operate, quick to respond, and start with the flick of a switch. Since they do not produce toxic exhaust fumes, they may be safely used inside buildings. This feature is an important one for both the operator and livestock.
Electric tractors are much quieter than those powered by internal combustion engines. This is important in reducing hearing loss among farmers and in minimizing noise which is particularly objectionable in urban fringe areas. More signficantly, quiet operation allows a skilled operator to hear and detect equipment problems and more carefully observe livestock health.
Energy concerns are paramount with today's farmer. This fact is evidenced by intense interest in alcohol, solar, wind and other alternative energy sources. The energy vulnerability of farm operators can be greatly reduced by the adoption of electric vehicles. Electricity is inherently more versatile than oil-derived fuels and can be generated from a great variety of energy sources. Although all energy costs will likely increase over the years, it is believed that oil-derived fuel costs will increase more rapidly than electrical costs. Studies conducted by the Department of Energy have concluded that with predicted technological advances, electric vehicles will be over 50% less expensive to operate than their internal combustion counterparts by 1990.
Electric tractors will undoubtedly play an increasingly important role in agricultural applications. Their advantages are well documented. There is a continuing need for electric tractors with different power output characteristics. The electric tractor should have a power-take-off which can be operated at a wide variety of speeds independently from the drive motor. The electric tractor should be reliable and require infrequent maintenance. In addition, the tractor should be safe, clean, quiet and easy to operate.